Rotor with permanent magnets

Abstract

The invention relates to a permanent magnet (1) for a dynamoelectric machine, in particular a dynamoelectric rotating machine (12), having a shape deviation (2, 6, 7) on a surface of the permanent magnet (1), wherein the shape deviation (2, 6, 7) comprises at least one raised portion (14) and at least one recess (15), wherein a height difference (h) between a highest point of the raised portion (14) and a lowest point of the recess (15) is at least 2% of a thickness (d) of the permanent magnet (1) and at most 20% of the thickness (d) of the permanent magnet (1).

Description

[0001] The invention relates to a rotor with permanent magnets for a dynamo-electric machine.

[0002] Metallic magnets used in permanent magnet synchronous machines are usually pressed, sintered, and finished, for example, by grinding or sawing. These manufacturing processes create a smooth surface on the permanent magnets. However, the surface structure of the permanent magnet influences its electrical resistance to the high-frequency currents generated during motor operation, which have an undesirable effect on the temperature and magnetic flux of the permanent magnets.

[0003] To increase ohmic resistance, magnets are currently also being segmented. However, this is very complex.

[0004] A technology for manufacturing rotors of synchronous machines with reduced superheating is known from publication RU 169 538 U1. The rotor of a permanent magnet synchronous machine, equipped with corrugations, is characterized by the fact that the magnets are corrugated on the outer surface facing the machine's air gap. The depth of the corrugations h is chosen to be equal to the wave width b, such that the step t is equal to t = h + b. The rotor can be equipped with non-magnetic bands for holding the permanent magnets, while the rotor bands are provided with corrugations similar to those on the magnets. The cooling surface of the magnets and bands is almost doubled, which reduces their superheating, and the corrugations increase the path length for eddy currents generated during machine operation, thus reducing heat generation in the magnets and band.

[0005] Publication JP 2008 251992 A discloses a powder injection molding process for the production of a permanent magnet with shape deviations of 200 to 600 µm.

[0006] Publication JP 2001 342502 A discloses a permanent magnet for a dynamoelectric rotary machine, having a shape deviation caused by grooves on a surface of the permanent magnet, wherein the shape deviation comprises at least one thickening and at least one depression, wherein a height difference between a highest point of the thickening and a lowest point of the depression is at least 2% of the thickness of the permanent magnet and at most 20% of the thickness of the permanent magnet.

[0007] German patent application DE 26 37 706 A1 discloses a permanent magnet for a dynamoelectric rotary machine, having a shape deviation that is conical in form. The increased surface area of ​​the permanent magnets increases their adhesive strength when bonded together.

[0008] Publication JP H09 308150 A discloses a rotor of an electric machine with slotted permanent magnets fixed to a shaft with a bandage thread for suppressing eddy currents.

[0009] The publication JP H06 205554 A discloses a slotted permanent magnet rotor for suppressing eddy currents. The slot width, depth, and spacing are primarily determined by the depth of eddy current penetration, which depends on the excitation frequency. In the case of small electric motors, the width is typically 0.3 mm or less, the depth 2 mm or less, and the spacing approximately 3 mm.

[0010] The invention is based on the objective of creating a rotor for a dynamoelectric rotary machine, wherein the permanent magnets of the rotor have an increased ohmic resistance.

[0011] The problem is solved by claim 1, i.e., a rotor for a dynamoelectric rotary machine comprising: a rotor pack, a plurality of permanent magnets, a bandage for fixing the permanent magnets to the rotor pack, wherein the bandage has a bandage thread, wherein the permanent magnets each have a shape deviation on a surface of the permanent magnet which is designed to receive the bandage thread, wherein the shape deviation comprises at least a conical thickening and at least one depression and wherein a height difference between a highest point of the thickening and a lowest point of the depression is at least 2% of the thickness of the permanent magnet and at most 20% of the thickness of the permanent magnet.

[0012] The invention offers the advantage that such a rough magnetic surface or structured magnetic surface increases the ohmic resistance to high-frequency alternating currents, and improved heat dissipation is also provided.

[0013] The described thickening and indentation increase the surface area of ​​the permanent magnet, which has a positive effect on heat dissipation. Furthermore, the indentation and thickening, or multiple indentations and multiple thickenings, lead to increased air turbulence, which also has a positive effect on heat dissipation.

[0014] An advantageous embodiment is one in which the height difference is at least 5% of the thickness of the permanent magnet and at most 20% of the thickness of the permanent magnet.

[0015] A typical permanent magnet is, for example, 1.5 mm to 5 mm thick. Using the example of a 3 mm thick permanent magnet, the height difference is at least 0.06 mm (corresponding to 2%), advantageously at least 0.15 mm, and at most 0.6 mm.

[0016] However, other magnet thicknesses are also conceivable.

[0017] An advantageous embodiment is one in which the height difference is at least 10 µm and at most 1,000 µm.

[0018] Preferably, the height difference is at least 10 µm and at most 500 µm.

[0019] An advantageous embodiment is one in which the shape deviation is formed as waviness and / or in the form of grooves and / or in the form of ridges and / or in the form of semicircular channels; a combination of the aforementioned shape deviations is possible.

[0020] A combination of shape deviations is further explained using the example of a rotor with external permanent magnets. In this example, a surface of the permanent magnet facing an air gap exhibits the shape deviation in the form of semicircular channels.

[0021] The surfaces of the permanent magnet that are arranged laterally, i.e., pointing towards a neighboring permanent magnet, may, for example, have grooves.

[0022] The shape deviation includes cone-shaped thickenings.

[0023] This shape deviation, also called conical structure, is particularly advantageous with regard to current displacement and creates a high ohmic resistance.

[0024] Preferably, the cone-shaped thickenings are evenly distributed over the surface of the permanent magnet.

[0025] It is also advantageous to have a design in which the shape deviation includes knurling.

[0026] Various knurling types are suitable for this purpose, such as left-hand knurling, right-hand knurling, knurling with parallel axes, grooves, knurling with raised tips, knurling with recessed tips, cross knurling with both raised and recessed tips, as well as circular knurling. A combination of the aforementioned knurling types is also conceivable.

[0027] An embodiment is also advantageous in which the width difference between two adjacent thickenings is at least 10 µm and at most 300 µm.

[0028] An advantageous embodiment is one in which the permanent magnet has at least one further shape deviation, wherein the height difference of the shape deviation is at least 10 µm and at most 100 µm, and wherein the height difference of the further shape deviation is at least 300 µm and at most 500 µm.

[0029] This advantageously combines two different shape deviations on or of the permanent magnet. For example, the surface facing the air gap can exhibit one shape deviation, and a lateral surface of the permanent magnet can exhibit another shape deviation.

[0030] Furthermore, it is also conceivable that, viewed axially, a front area of ​​the surface, which points towards the air gap, exhibits the shape deviation and a rear part the further shape deviation.

[0031] The shape deviation features depressions that are wide and deep enough to preferably accommodate the entire bandage thread. Partial absorption is also possible.

[0032] The bandage thread, for example, contains at least one carbon fiber and / or at least one glass fiber.

[0033] For this purpose, the shape deviation advantageously comprises a plurality of grooves, wherein the grooves are arranged at least substantially equidistantly, wherein the grooves have a height difference of at least 300 µm and at most 500 µm, and wherein the grooves have a width difference of at least 100 µm and at most 300 µm.

[0034] The bandage thread should ideally have a diameter of at least 100 µm and at most 300 µm. This allows the bandage thread to be easily laid into the grooves.

[0035] This is advantageous because it means that the bandage thread barely protrudes from the permanent magnet, or not at all.

[0036] This has the advantage that the effective magnetic air gap can be reduced. No additional space is required for the bandage.

[0037] The problem can also be solved by a dynamo-electric machine, in particular a dynamo-electric rotary machine, comprising a rotor.

[0038] The problem can also be solved by a method for producing such a permanent magnet, wherein the permanent magnet is produced by means of powder injection molding.

[0039] Powder injection molding is also known as the "MIM process" (English for Metal Injection Moulding).

[0040] Powder injection molding advantageously comprises the following, in particular successive, process steps: feedstock production, injection molding, debinding and sintering.

[0041] The permanent magnet produced in this way can be further treated.

[0042] Feedstock production is advantageously achieved by mixing a metal powder, in particular magnetic powder, with a plastic, preferably a thermoplastic. The mixture can be referred to as feedstock.

[0043] The feedstock may also contain other substances, such as binders or organic binders.

[0044] Warming the feedstock is beneficial.

[0045] Advantageously, the feedstock is then injected afterwards to preserve the permanent magnet.

[0046] The permanent magnet is advantageously exposed to anisotropy during the forming process to obtain an anisotropic permanent magnet. During injection molding, a magnetic field is advantageously applied briefly.

[0047] Advantageously, a demagnetization process follows.

[0048] The invention will now be described and explained in more detail with reference to the exemplary embodiments shown in the figures. The figures show: FIG 1 a rotor, FIG 2 a further embodiment of the rotor, FIG 3 a shape deviation, FIG 4 a further embodiment of the shape deviation, FIG 5 a dynamoelectric machine, FIG 6 a further embodiment of the permanent magnets, FIG 7 a method for manufacturing the permanent magnet.

[0049] FIG 1 The figure shows a rotor 10. The rotor 10 has a plurality of external permanent magnets.

[0050] The permanent magnets 1 exhibit a shape deviation 2.

[0051] FIG 2 shows another embodiment of rotor 10.

[0052] The rotor 10 has a plurality of external permanent magnets 1, which are bandaged to fix them to the rotor assembly. For this purpose, a bandage thread 5 has been wound clockwise around the permanent magnets 1 and the rotor 10 in the figure.

[0053] The bandage thread 5 is positioned as shown in FIG 3 shown, advantageously in semicircular recesses 7.

[0054] The in FIG 3 The permanent magnet 1 shown has a shape deviation which is formed on a surface pointing towards the air gap and is formed in the form of semicircular depressions.

[0055] The indentations are designed in such a way that the bandage thread 5 can be accommodated.

[0056] There are several possibilities here. The indentations 7 can be so deep that the bandage thread, with a surface facing the air gap, is flush with the thickening 14.

[0057] However, as shown in this figure, only a partial absorption of the bandage thread through the semicircular depression 7 is conceivable.

[0058] The permanent magnet 1 also exhibits a further shape deviation 2 on its underside and on both side surfaces. This shape deviation 2 is represented as roughness in the figure.

[0059] The figure also shows a thickness d of the permanent magnet 1, a height h of the thickening 14 and a width b of the depression 15.

[0060] FIG 4 shows another embodiment of the shape deviation 2.

[0061] The surface of the permanent magnet 1 has a plurality of cone-shaped thickenings 8.

[0062] Conical thickenings 8 are advantageous for the surface or structure of a bandage and also represent an easy-to-form shape in an injection mold.

[0063] FIG 5 Figure 12 shows the dynamoelectric machine 12, comprising a stator 11, a shaft 3 and the rotor 10.

[0064] FIG 6 shows another embodiment of the permanent magnet 1.

[0065] This figure features a knurling 16. The knurling 16 is also a form of shape deviation 2.

[0066] The invention offers many advantages. Due to the reduced currents in the permanent magnets 1, the permanent magnets 1 heat up less. Therefore, less expensive magnetic materials can also be used.

[0067] Furthermore, the power and torque density of the motors is increased. The currents are advantageously reduced by the skin effect.

[0068] Furthermore, the increased surface area of ​​the permanent magnets 1 results in improved heat dissipation, leading to cooler magnets. This also has a positive effect on costs and motor performance.

[0069] The targeted surface structure for receiving the bandage thread results in a smaller magnetically effective air gap and thus in higher magnetic inductions, which is associated with an increased power and torque density.

[0070] Furthermore, the powder injection molding manufacturing process allows for a high degree of freedom regarding shape deviations. The permanent magnets 1 can be flexibly designed.

[0071] FIG 7 shows a method for manufacturing the permanent magnet 1.

[0072] Powder injection molding advantageously has the following, in particular successive, process steps: In a process step S1, feedstock production takes place.

[0073] Feedstock production is advantageously achieved by mixing a metal powder, in particular magnetic powder, with a plastic, preferably a thermoplastic. The mixture can be referred to as feedstock.

[0074] The feedstock may also contain other substances, such as binders or organic binders.

[0075] Warming the feedstock is beneficial.

[0076] In process step S2, injection molding takes place.

[0077] In S2, the feedstock is injected to maintain the permanent magnet.

[0078] The permanent magnet is advantageously exposed to a directed magnetic field during the forming process to obtain an anisotropic permanent magnet. During injection molding, a magnetic field is preferably applied briefly.

[0079] In process step S3, debinding takes place, i.e., the removal of binding agent.

[0080] Debinding is preferably carried out at a temperature of 200°C to 400°C.

[0081] Sintering takes place in process step S4.

[0082] Sintering preferably takes place at a temperature of 900°C to 1100°C.

[0083] This ensures that the permanent magnet 1 is firmly bonded.

Claims

1. Rotor (10) for a dynamoelectric rotary machine (12), having: - a rotor stack, - a plurality of permanent magnets (1), - a binding for fixing the permanent magnets (1) to the rotor stack, wherein the binding has a binding thread (5), wherein the permanent magnets (1) each have a shape deviation (2, 6, 7) at a surface of the permanent magnet (1), which is embodied for receiving the binding thread, characterised in that the shape deviation (2, 6, 7) comprises at least one conical thickening (8, 14) and at least one indentation (15) and a height difference (h) between a highest point of the thickening (14) and a lowest point of the indentation (15) is at least 2% of a thickness (d) of the permanent magnet (1) and at most 20% of the thickness (d) of the permanent magnet (1).

2. Rotor according to claim 1, wherein the height difference (h) is at least 5% of the thickness (d) of the permanent magnet (1) and at most 20% of the thickness (d) of the permanent magnet (1).

3. Rotor according to one of the preceding claims, wherein the height difference (h) is at least 10 µm and at most 1,000 µm.

4. Rotor according to one of the preceding claims, wherein the height difference (h) is at least 10 µm and at most 500 µm.

5. Rotor according to one of the preceding claims, wherein the shape deviation comprises a waviness and / or grooves and / or furrows and / or semi-circular channels.

6. Rotor according to one of the preceding claims, wherein the shape deviation comprises a knurling.

7. Rotor according to one of the preceding claims, wherein a difference in width between two adjacent thickenings is at least 10 µm and at most 300 µm.

8. Rotor according to one of the preceding claims, wherein the shape deviation comprises a plurality of grooves, wherein the grooves are arranged at least substantially equidistantly, wherein the grooves have a height difference, which is at least 300 µm and at most 500 µm, wherein the grooves have a difference in width, which is at least 100 µm and at most 300 µm.

9. Dynamoelectric machine, in particular dynamoelectric rotary machine, having a rotor according to one of claims 1 to 8.

10. Method for producing a rotor (10) according to one of claims 1 to 8, wherein the permanent magnet is produced by means of powder injection moulding.

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